Security has been a major vote winner. An Economist/YouGov poll found that 51 percent of Republicans believe the US will be safer from terrorism at the end of his term.

The budget may also be seen as a signal to the world that Trump's United States may be less engaged and will put "America first".

Diplomats and some former defence officials have already sounded a warning that less spending on things such as democracy promotion and humanitarian aid will spell more trouble, and military spending, down the road.

More than 120 retired generals and admirals recently signed a letter warning "that many of the crises our nation faces do not have military solutions alone".

They cited Jim Mattis, now defence secretary, as once saying: "If you don't fully fund the State Department, then I need to buy more ammunition."

'Drastic cuts'

The Environmental Protection Agency, which helps monitor air, water and other standards, will also see significant cuts.

That is in keeping with Trump's promise to gut regulation.

"We believe that the core functions [of the EPA] can be satisfied with this budget," said Mulvaney.

On Wednesday, Trump travelled to Detroit, the home of the US car-manufacturing industry and announced that he will freeze targets to limit future vehicle emissions.

Steve Bannon, Trump's top adviser, has promised a broader "'deconstruction of the administrative state".

But Trump's plan is already facing criticism from Democratic politicians.

"It will prescribe drastic cuts in many of the programmes and agencies that keep America safe, whether it's environmental programmes, whether it is food safety, drug safety," said John Yarmuth, Kentucky representative.

The senior member on the House of Representatives budget committee speculated that the proposal could be a negotiating position, an opening salvo in Trump's "art of the deal".

"If they want to negotiate with the health and safety and future of the American people, then that's pretty cynical," he said.